1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head that includes a waveguide, a plasmon generator, and a magnetic pole, and to a method of manufacturing the same.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and magnetic recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the magnetic recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the magnetic recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the aforementioned problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a magnetic recording medium having high coercivity. When writing data, a write magnetic field and heat are applied almost simultaneously to the area of the magnetic recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the magnetic recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with light. The light for use in generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
The plasmon generator that generates near-field light by direct irradiation with light is known to exhibit very low efficiency of transformation of the applied light into near-field light. The energy of the light applied to the plasmon generator is mostly reflected off the surface of the plasmon generator, or mostly transformed into thermal energy and absorbed by the plasmon generator. The plasmon generator is small in volume since the size of the plasmon generator is set to be equal to or smaller than the wavelength of the light. The plasmon generator therefore shows a significant increase in temperature when it absorbes the thermal energy.
Such an increase in temperature causes the plasmon generator to expand in volume and protrude from the medium facing surface. This increases the distance from the read head section and the write head section to the surface of the magnetic recording medium, thereby possibly causing degradation of the characteristics of the thermally-assisted magnetic recording head. Furthermore, an increase in temperature of the plasmon generator can degrade the magnetic property of a magnetic pole for producing a write magnetic field in the write head section, and can thereby degrade the characteristics of the write head section.
To address this problem, there has been proposed such a technology that the surface of the core of the waveguide and the surface of the plasmon generator are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the excited surface plasmons. The technology is disclosed in, for example, U.S. Patent Application Publication No. 2011/0058272 A1.
The aforementioned technology allows the light propagating through the core to be transformed into near-field light with high efficiency, and also allows the plasmon generator to be prevented from excessively increasing in temperature because the plasmon generator is not directly irradiated with the light propagating through the core.
For a thermally-assisted magnetic recording head, it is necessary that the position of occurrence of the write magnetic field and the position of occurrence of the near-field light be located in close proximity to each other in the medium facing surface. Here, the following problem arises if such a configuration is employed that the surface of the core of the waveguide and the surface of the plasmon generator face each other with a gap therebetween, and the position of occurrence of the write magnetic field and the position of occurrence of the near-field light are located in close proximity to each other. That is, in such a case, both the core and the magnetic pole need to be located near the plasmon generator. It follows that the magnetic pole is located near the core. The magnetic pole is typically made of a magnetic metal material. The presence of such a magnetic pole near the core causes the problem that part of the light propagating through the core is absorbed by the magnetic pole and the use efficiency of the light propagating through the core thereby decreases.
On the other hand, to reduce the track width of a magnetic recording medium for higher recording density, it is required that the near-field light be small in spot diameter on the magnetic recording medium. U.S. Patent Application Publication No. 2011/0058272 A1 discloses a structure that is achieved by forming a groove in a dielectric layer disposed above the top surface of the core such that the groove is V-shaped in cross section parallel to the medium facing surface, and then forming a dielectric film, a plasmon generator, and part of a magnetic pole in this order in the groove. In this structure, the plasmon generator has two sloped surfaces that form a V-shape in a cross section parallel to the medium facing surface, and an edge part formed by the two sloped surfaces intersecting each other. The edge part faces toward the top surface of the core, with a gap of a predetermined size interposed between the edge part and the top surface of the core. An end of the edge part located in the medium facing surface serves as a near-field light generating part.
In the foregoing structure, the light propagating through the core is totally reflected at the top surface of the core. This causes evanescent light to occur from the top surface of the core. Then, surface plasmons are excited at least on the edge part of the plasmon generator through coupling with the evanescent light. The surface plasmons propagate along the edge part to the near-field light generating part, and near-field light is generated from the near-field light generating part based on the surface plasmons. This structure allows the surface plasmons excited on the plasmon generator to propagate to the near-field light generating part with efficiency. This structure also allows the position of occurrence of the write magnetic field and the position of occurrence of the near-field light to be close to each other. Furthermore, since the plasmon generator is disposed between the core and the magnetic pole, it is possible to prevent part of the light propagating through the core from being absorbed by the magnetic pole.
However, the following first and second problems have been found with the aforementioned structure. The first problem will be described first. The plasmon generator in the aforementioned structure has such a configuration that the surface plasmons are not allowed to exist only on the edge part but are distributed to extend from the edge part to a portion of each of the two sloped surfaces located in the vicinity of the edge part. Consequently, the aforementioned structure causes the near-field light to have a large spot diameter on the magnetic recording medium, thereby making it difficult to reduce the track width. This is the first problem.
The second problem will now be described. In the aforementioned structure, the efficiency of transformation of the light propagating through the core into near-field light varies according to the distance between the edge part and the top surface of the core. The second problem is that when thermally-assisted magnetic recording heads are mass-produced, the distance between the edge part and the top surface of the core varies greatly from one head to another, and as a result, the efficiency of transformation of the light propagating through the core into near-field light varies greatly from one head to another. The reason for this will be described below. Typically, thermally-assisted magnetic recording heads are manufactured in the following manner. First, components of a plurality of thermally-assisted magnetic recording heads are formed on a single wafer to fabricate a substructure including a plurality of pre-head portions aligned in rows, the plurality of pre-head portions being intended to later become individual thermally-assisted magnetic recording heads. Next, the substructure is cut to separate the pre-head portions from each other into individual thermally-assisted magnetic recording heads. To manufacture the thermally-assisted magnetic recording heads having the aforementioned structure, as described previously, a groove that is V-shaped in cross section parallel to the medium facing surface is formed in the dielectric layer disposed above the top surface of the core, and then the dielectric film, the plasmon generator, and part of the magnetic pole are formed in this order in the groove. Dry etching such as ion milling or reactive ion etching is employed to form the groove. In the case of forming the components of a plurality of thermally-assisted magnetic recording heads on a single wafer, there occur great variations in the position and shape of the bottom of the groove. This causes the distance between the edge part and the top surface of the core to vary greatly from one head to another, and as a result, the efficiency of transformation of the light propagating through the core into near-field light varies greatly from one head to another.